Suppressing warnings for clashing note columns
If notes from two voices with stems in the same direction are placed at
the same position, and both voices have no shift or the same shift
specified, the error message
warning: ignoring too many clashing note columns will appear
when compiling the LilyPond file. This message can be suppressed by
setting the 'ignore-collision property of the NoteColumn
object to #t. Please note that this does not just suppress
warnings but stops LilyPond trying to resolve collisions at all and so
may have unintended results unless used with care.
ignore = \override NoteColumn.ignore-collision = ##t
\relative c' {
\new Staff <<
\new Voice { \ignore \stemDown f2 g }
\new Voice { c2 \stemDown c, }
>>
}